Apparatus for forming cross-bottom folding in bag manufacture

ABSTRACT

In bag-making machinery, apparatus for forming cross-bottom folding on the ends of open-ended flattened tube sections of bag material fed transversely of the sides of the tube sections, the apparatus comprising two spreaders effective to enter and spread the ends of the tube sections and synchronously rotatable about respective shafts which are inclined to each other symmetrically with respect to the feeding plane and which are themselves pivotable about respective points disposed symmetrically with respect to the feeding plane, whereby to improve the spreading operation.

States Patent [191 uclihermann et al.

[ Apr. 16, 1974 APPARATUS FOR FORMING CROSS-BOTTOM FOLDING IN BAG MANUFACTURE Inventors: Gustav Kuckhermann; Richard Feldkamper, .both of Lengerich of Westphalia, Germany Windmoller.& Holscher, Lengerich of Westphalia, Germany Filed: Dec. 21, 1971 Appl. No.: 210,468

Assignee:

Foreign Application Priority Data Dec. 21, 1970 Germany 2062944 us. Cl. "93/28 Int. Cl B3lb 1/76 Field of Search 93/28, 53, 22, 30

References Cited UNITED STATES PATENTS 5 1955 Rawe ..93/28 3,006,256 10/1961 2,712,275 7/1955 Gramegna 2,888,859

6/1959 Dambacher 93/28 Primary Examiner-Andrew R. Juhasz Assistant ExaminerLeon Gilden Attorney, Agent, or Firm-Fleit, Gipple & Jacobson 57 ABSTRACT In bag-making machinery, apparatus for forming cross-bottom folding on the ends of open-ended flattened tube sections of bag material fed transversely of the sides of the tube sections, the apparatus comprising two spreaders effective to enter and spread the ends of the tube sections and synchronously rotatable about respective shafts which are inclined to each other symmetrically with respect to the feeding plane and which are themselves pivotable about respective points disposed symmetrically with respect to the feeding plane, whereby to improve the spreading operation.

21 Claims, 11 Drawing Figures *Wjagu g Rawe 1.93/28 PMENTEDAPR 16 1974 3 803L989 SHEET 2 0F 6 PATENTED APR 16 I974 SHEET 3 OF 6 APPARATUS FOR FORMING CROSS-BOTTOM FOLDING IN BAG MANUFACTURE The invention relates to an apparatus for forming cross-bottom folding at the ends of flattened tube sections which are to be made into bags or sacks and the ends of which are fed in a plane in a direction transversely to the sides of the tube sections.

German Pat. No. 714,028 discloses such an apparatus comprising two sickle-shaped spreaders which are effective to enter and spread the ends of the tube sections and which are synchronously rotatable about shafts extending at an inclination to one another symmetrically with respect to the feeding plane of the ends to be spread. The tube sections are successively fed past the rotating spreaders and the arrangement is such that, when the spreaders are closest to one another on curs particularly when the material of the tube sections,

which may be of single or multiple ply, is not very stiff, e.g., when the material is thin paper or flexible plastics film. The spreaders entering the ends of the tube sections only make point contact with the bagsides to be spread and, with flexible bag material, this means that the ends will not be pulled open over their entire area and can easily become creased and crumpled. This problem is more pronounced for large spreading movements of the spreaders in the case of forming wide cross-bottoms. Crumpled cross-bottom folding is useless and gives rise to interruptions in the operation of the bag-making machine if the defective tube section is not removed in time. Similar disruptions occur during laying of the rear triangle of the base if its formation is allowed to take placeautomatically as-in the aforementioned German specification. With flexible bag-material exact formation of the front triangle of the base may likewise prove difficult. Similar disadvantages occur with stiffer tube sections that are being processed at higher speeds. The spreading effected by the'si'ckleshaped spreaders can thus not simply be increased by a corresponding alteration in the included angle between the rotary shafts of the spreaders.

The invention aims to provide an improved apparatus which will satisfactorily spread the ends of the tube sections without presenting difficulties during insertion of the spreaders in the open tube ends.-

According to the invention, there is provided an apparatus for forming cross-bottom folding at the ends of flattened tube sections which are to be made into bags or sacks and the ends of which are fed in a plane in a direction transversely to the sides of the tube sections,

the feeding plane of the ends to be spread, said'rotary shafts being pivotable during each work cycle about re spective pivot points disposed symmetrically with respect to the feeding plane.

By pivoting the rotary shafts, the spreaders can, whilst they enter an open end of the tube section and whilst they pull this end open, have any desired spreading movement imparted to them to conform with the properties of the bag material and the widths of the ends to be pulled open.

Preferably, the spreaders are sickle-shaped and attached to the rotary shafts by their sickle stems. This attachment may be releasable so that the stems can be adjusted lengthwise of the rotary shafts to change the diameter of the circlesdescribed by the sickles during their rotation.

The rotary shafts are preferably pivotable during the spreading operation, in the sense of increasing their angles of inclination, about respective pivot shafts which are preferably parallel to the feeding direction of the tube sections and the axis of each of which passes through one of the aforementioned pivot points. This causes the spreaders or sickles to be moved apart substantially normal to the feeding plane of the ends of the tube sections to be spread, thereby giving rise to a spreading movement in addition to the spreading that is already caused by rotation of the spreaders about their inclined axes, the sudden increase in the angle of inclination permitting the front corner fold to be laid properly for any desired width of bag. The increase in the angle of inclination of the rotary axes of the spreaders is also effective to cause the trailing ends of the sickles to execute a spreading movement in the same direction as the ends of the tube section are being pulled open. This spreading movement of the trailing sickle ends ensures that they will sweep over and flatten the bag walls after the rear triangle of the base has been formed and they will extend right into the corners of the triangle. In this way the rear triangles will also be formed accurately without the danger of crumpling.

-In one form of the invention, pivotal movement to increase the angle included between the rotary shafts of the spreaders is effected in that bearings for the rotary shafts are connected to respective mountings which are pivotable about the pivot shafts and can be driven in the sense of providing the desired pivotal movement. For this purpose the mountings may intereng'age by means of gear teeth and thereby be positively intercoupled, a pivoting drive being applied to one of the mountings.

Pivotal movement of the rotary shafts during each work cycle is also possible along a substantially conical path about a straight line joining the pivot points'in the sense of displacing an imaginary point at which the spreaders come closest to one another during their rotation. Such pivoting likewise permits movement of the spreaders during each work cycle to be altered in the sense of permitting easy entry of the spreaders into the tube sections and proper formation of the base folding.

It is particularly advantageous if the point of closest approach of the spreaders is displaced into each tube section end during entry of the spreaders into each tube section. This means that the spreaders, which reach their point of closest approach before entering the preopened ends of the tube sections, do not commence their spreading operation during entry into the ends of the tube sections but remain close to one another until they start their outwards movement during which they effect spreading of the base. If the point of closest approach is displaced during each spreading operation against the direction of rotation of the spreaders, then the points of the sickle-shaped spreaders will be additionally moved apart to facilitate spreading to the fullest extent. By swinging the rotary shafts of the spreaders backwards, the spreaders will sweep over the side wall portions that are to be drawn open, such sweeping movement being executed symmetrically with respect to the feeding plane of the tube sections and transversely to the direction of rotation of the spreaders in the direction of drawing the tube sections open. The sweeping movement causes the spreaders to smooth the wall portions of the ends of the tube sections that are to be pulled open to form cross-bottoms and thus creasing and crumpling of the bag material is avoided. On the other hand, the danger of crumpling during entry of the spreaders into the tube sections is avoided by the aforementioned forward pivotal movement of the rotary shafts along a substantially conical path upon commencement of the work cycle.

Such forward pivoting of the rotary shafts may be achieved if a bearing for each of the rotary shafts is attached to a mounting member which is pivotable on a pivot shaft having an axis extending through the two pivot points and which is reciprocatable in accordance with the desired displacement of the point of closest approach. In this form of the invention only the previously described forward and return displacement'of the point of closest approach are possible during each work cycle whereas the mutual inclination of the rotary shafts cannot be effected or can be effected only when the apparatus is inoperative.

Pivotability of the rotary shafts to all sides to change the inclination of the shafts as well as the forward and return displacement of the point of closest approach during each work cycle may be achieved if each rotary shaft is pivotable about two perpendicular pivot shafts which pass through one of the pivot points and to which the respective rotary shaft is also perpendicular. The three perpendicular shafts extending through the pivot point form the shafts of a spacial coordination system in which the respective rotary shaft of the spreader can execute any desired movement about the pivot point during each work cycle under the influence of appropriate drive means. It is of particular advantage in such a construction if the point of closest approach of the sickle-shaped spreaders is displaced into the end of the tube section whilst the spreaders are being inserted into the pre-opened end and the spreaders are then suddenly moved apart by increasing the angle included between their rotary shafts.

To effect such all-sided adjustability in the case of the construction where the bearings of the rotary shafts are connected to mountings which are pivotable about the pivot shafts, the bearings of the rotary shafts are attached to the respective mountings by supporting arms pivotable about pivot shafts which extend lengthwise of the mountings and the axes of which extend through the respective pivot points. By swinging the supporting arms about these shafts, the point of closest approach of the spreaders is changed along their circular path in the feeding plane of the ends of the tube sections. However, if the pivot shafts of the supporting arms do not coincide with the straight line joining the two pivot points, it is necessary at the same time as pivoting the supporting arms to effect a change in the inclination of the rotary shafts by pivoting the mountings about the pivot shafts so as to maintain the spacing of the spreaders at the point of closest approach.

The rhythmic pivotal drive of the pivot shafts for the supporting arms can be effected by means of bevel gears on the pivot shafts of the supporting arms engaging with bevel gear segments which are pivotable about respective stationary axes and which are provided with a pivot drive operative in sequence with the work cycle.

The bearings for the rotary shafts may be attached to the mounting member or mountings by supporting arms having slots which are concentric with the pivot points and by means of which the inclination of the spreaders is adjustable. In this way the desired basic inclination of the rotary shafts can be set whilst the apparatus is stationary, possibly in conjunction with the previously described longitudinal adjustment of the sickle stems of the rotary shafts.

Each rotary shaft may be driven by an articulation disposed at a respective one of the pivot points. If the articulations are in the form of universal joints, the irregular rotary speed occasioned by such universal joints by reason of their construction can be utilised advantageously. To ensure that the spreaders move at substantially the same constant feeding speed of the tube sections during formation of the cross-bottom, the spreaders of known apparatuses are driven by a variable drive which decreases their circumferential speed during entry into the tube sections and decreases the speed as they move out again so that their circumferential speed component in the feeding direction of the tube sections is substantially the same as the feeding speed. The universal joints that may be used in the construction of the present invention now only need to be connected to the rotary shafts at such an angular position that the circumferential speed of the spreaders will be a minimum whilst they are passing through the open end of a tube section. In many cases this will make it unnecessary to provide a special variable drive. Where it is not possible to dispense with such a variable drive it will in any case be sufficient to use a simple variable drive providing only a slight speed variation, the angular position of the drive relatively to the universal joints being selected so that its speed variation is, as required, added to or subtracted from the speed variation of the universal joints so as to achieve the variable circumferential speed of the spreaders necessary for obtaining uniform running of the spreaders and the tube section at the point of closest approach.

The universal joints may be driven separately or through a single drive but it is preferred if they are driven by a connecting shaft which interconnects the universal joints and carries a gear.

Of course it is also possible to employ other drive means for the rotary shafts. For example, each rotary shaft may comprise a drive which is pivotable together therewith, the two drives being synchronised with one another.

Examples of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a part-sectional front elevation, taken on the line I-I in FIG. 2, of a folding apparatus for the crossbottoms of bags and viewed in the feed direction of the bag blanks;

FIG. 2 is a side elevation of the FIG. 1 apparatus taken in the direction "-11 in FIG. 1;

FIG. 3 is an elevation of the apparatus taken in the direction IIIIII of FIG. 1;

FIGS. 4 to 8 are diagrammatic views showing different stages in the sequence of operation of the apparatus, FIGS. 4, 6 and 8 being side elevations and FIGS. 5 and 7 plan views;

FIG. 9 is a front elevation of a simplified embodiment of the apparatus for carrying out the folding operations indicated in FIGS. 4 to 7;

FIG. is a plan view of the FIG. 9 apparatus, and

FIG. 11 is a diagram of a further embodiment repre-" senting a modification of the FIGS. 1 to 3 apparatus.

Referring to FIGS. 1 to 3, the apparatus for drawing open the ends of tube sections to form the crossbottoms of bags comprises two sickle-shaped spreaders ll, 1' which will hereinafter be referred to simply as sickles. These sickles rotate synchronously about shafts 2, 2 which are symmetrical with respect to the feeding plane E'-E of tube sections S that are to be provided with the cross-bottom folding and which are inclined to one another at an angle 2a. The direction of rotation of the sickles is such that, when they are at a point P of closest approach to one another, they will be moving in the same direction as the direction a'in which the tube sections are fed along the plane EE. The angle 2a between the rotary shafts 2, 2' of the sickles and the diameter of the sickles 1, l are chosen so that the circular paths executed by thesickles touch one another at the point P (which is located in the feeding plane E--E) or are spaced only a few millimeters apart at this point. The entire arrangement of the pair of sickles is, as shown in FIG. 5, such that the point P lies as closely as possible to the edge at the open end of each tube section being moved past the sickles in the direction of the arrow a, the end of the tube section that is to form the cross-bottom base projectingfrom between two stationary guide rails 3, 3" to an extent indicated by the arrows y.

The two rotary shafts 2, 2 are driven synchronously to one another in the feed direction a of the tube sections by means of universal joints 4, 4' which are symmetrical to the feeding plane EE, the universal joints being driven through a common gear 5 and a pinion 6. The universal joints are mounted in pivot arms 7, 7 of which the pivot shafts 12, 12' pass through a respective one of the pivot points K, K of the universal joints. This mounting of the rotary shafts 2, 2' permits pivotal movement 0, c of the sickles l, 1" about the respective pivot points. The pivot shafts 12, 12' are mounted on pivotable mountings 8, 8' of which the pivot shafts 9, 9 are stationary, extend parallel to the feed direction a of the tube sections and pass through the associated pivot points K, K of the universal joints. By means of the pivotable mountings 8, 8, pivotal movements b, b" independent of the pivotal movements c, c' are possible by the sickles 1, l transversely to the feed direction a of the tube sections.

The two mountings 8, 8' have gear teeth 10, 10' which interengage in the feed plane E--E of the tube sections. They are driven by a push bar 11, for example through a thrust cam (not shown) which moves in synchronism with the bag-making machine. By appropriately shaping the cam of this thrust cam drive, any desired pivotal movement b, bf of the sickles can be obtained about their respective pivot points symmetrical with respect to the feed plane E-E and transversely to the feed direction a of the tube sections S.

The pivot arms 7, 7 are fixed to their shafts l2, l2

are driven through a push bar 17 by, for example, a

thrust cam (not shown) which rotates in sequence with the operating cycle of the bag-making machine. By appropriately shaping the thrust cam of this thrust cam drive, the sickles 1, 1 can execute any desired pivotal movements 0, c symmetrical with respect to the feed plane E-E about the respective pivot points. Slots 34, 34' in the supportingarms 7, 7' permit the initial setting of the angle of inclination a to be effected when the apparatus is at a standstill.

Since both pivotal movements b, b' (about the shafts 9) and c, 0' (about the shafts 112) are independent from one another, they can be combined to any desired resultant pivotal movements by appropriately shaping their thrust cams.

When laying the crossbottoms, especially in the case of bags of flexible film, the aforementioned pivotability of the rotating sickles is made use of in the manner represented in FIGS. 4 to 8.

' According to FIGS. 4 and 5, the rotary shafts 2, 2' of the sickles are inclined to one another in the plane F-F at such an angle 20: that the point P of contact or closest approach of the rotating sickles is disposed directly in front of the edge atthe open end of the tube sections S moving in the feeding direction a. The spacing x-l-y of the sickles 1,1 from the pivot points K, K of the universal joints is selected so that the sickles enter each tube section by the depth Y necessary for forming a cross-bottom base. Along a folding edge for the cross-bottom base, each tube section is guided between the guide rails 3, 3'. The end of the tube section is pre-opened in the manner indicated in FIG. 4 shortly before reaching the rotating sickles, for example by means of suckers (not shown), so as to facilitate free entry into the tube section of the sickles which are closely juxtaposed at the point P (see FIG. 5). Moving apart of the sickles by a distance 2 whilst they are together passing through the tube section is chosen by appropriate selection of the sickle diameter and the included angle 2a of inclination of their shafts 2, 2' and is kept so small thatcrumpling and creasing of the bag walls is avoided during entry of the sickles into the tube sections. The angle 2a is set by pivoting the mountings 8, 8 in the direction I), b to suit the diameter of the I curved portion of the sickles. The sickles l, 1' themselves have their stems releasably secured in hubs of the rotary shafts 2, 2. For the purpose of adapting the sickles to various dimensions of cross-bottoms, the sickles may be displaced in their hub within certain limits and they can be replaced by other sickles. The larger separation z of the sickles (see FIG. 6) required for the proper formation of the front triangle D of the base can be obtained by swinging the sickles back along their common circular rotary path R in the feed plane E-E of the tube sections by an angle 8 (FIG. 7). This backward swinging displaces the point P of closest approach of the sickles along the circular path from the edge at the open end of the tube section S to the position P and this of course results in an increase of the sickle separation from z to Z Backward swinging of the sickles is brought about by pivoting the rotary shafts 2, 2' along arcuate paths symmetrical with respect to the feed plane E-E about a common axis A which passes through the pivot points K, K and is normal to the feed plane EE. This arcuate pivoting of the rotary shafts of the sickles is produced as a resultant of the previously described pivotal movements b, b and c, c by appropriately shaping the thrust cams that move the mountings 8, 8 and the bevel gear segments 14, 14'. Separation of the sickles from 2 to Z takes place towards the end of their entry into the tube section and causes the sickles to effect an upwardly and downwardly directed sweeping movement against the corners of the front base triangle D that is being formed by the bag sides being pulled taut during spreading. This accurate formation of the base triangle takes place even if the bag material is flexible, such as of plastics film. The base triangle is finally folded by pairs of pressure rollers 18, 18 (FIGS. 6 and 7) between which the base triangle is passed.

A different and preferred way of improving the spreading operation resides in suddenly increasing the angle 2a of inclination of the rotary shaft during each work cycle after entry of the sickles in the tube section ends by appropriate pivotal movements b, b'. Such adjustment is diagrammatically illustrated in FIG. 8 (where the sickles 1, 1' are shown in chain-dotted lines before adjustment and in full lines after adjustment) and makes it possible to separate the'sickles substantially perpendicular to the plane EE. This means that true spreading of the tube section end is effected. Since the sickles rotate about oblique shafts 2, 2', they constantly move apart during their rotation to open the end of the tube section. A sudden increase in the angle a by means of the adjustments b, b can then finally shape and align the front corner fold. After the trailing ends of the sickles have passed into the tube section, they participate in the spreading of the leading ends of the sickles and thereby shape the rear comer fold by executing a sweeping movement along the bag sides towards the comers of the rear base triangle D thereby pulling the bag sides taut and accurately shaping the rear base triangle. The required pivotal movement b, b is, as already described, obtained by appropriately shaping the thrust cams controllingthe mountings 8, 8', it being possible at the same time to bring about a slight additional pivotal movement 0, c by moving the bevel gear segments 14, 14'.

Entry of the sickles l, 1' into the tube section can, if necessary, be facilitated if at the instant of insertion they are swung forwardly into the open end of the tube section along their circular rotary paths R in the feed direction a so that their point P of closest approach is displaced into the tube section, i.e., opposite to the previously described movement from P to P In this way separation of the sickles is postponed until they have entered the tube section to such an extent that they can no longer cause crumpling or creasing of the tube section. Only then are the sickles swung backwardly as already described to displace the point P to the position P, or to increase the included angle 2a between the sickle shafts 2, 2' for the purpose of more intense spreading of the cross-bottom base. Similarly, forward swinging of the sickles for the purpose of displacing the point P into the tube section can be readily effected by appropriately shaping the thrust cams controlling the mountings 8, 8' and the gear segments l4, l4. Pivotal movement c, 0' about the shafts 12, 12' alone is sufficient to displace the point P forwardly and backwardly along the circular path R only if the shafts 12, 12' coincide with the straight line A. If this is not the case, then during each adjustment c, c the spacing of the rotary path of the sickles 1, 1' would be changed and would have to be corrected by an adjustment [1, b.

FIGS. 9 and 10 illustrate a considerably simplified embodiment which permits only the adjustment c, c, an increase in the included angle 2a between the rotary shafts during operation of the apparatus being dispensed with. Since the pivotal movements b, b do not occur, the adjustment 0, 0 must take place about the axis A-A. The two universal joints are driven through a shaft 35 from a common gear. The rotary shafts of the sickles are mounted in bearings 33 attached to a common supporting member 31, 31 by supporting arms 33, 33', the slots 30, 30' permitting adjustment of the angle 2a whilst the apparatus is stationary. Forward and backward displacement of the point P of closest approach is possible during operation of the apparatus in the manner already described with reference to FIGS. 1 to 3. The thrust bar 29 is driven in sequence with the operating cycle of the bag-making machine by a pivotal drive (not shown), e.g., a thrust cam.

FIG. 11 shows a diagram representing a modification of the FIGS. 1 to 3 apparatus. This illustration makes it particularly clear that the angle a is adjustable by changing the angle B by adjusting the pivot arm 7 in the bearing 25. FIG. 11 also shows that the pivot radius of the sickles 1, l' is adjustable by displacing and then securing the stems 28, 28 of the sickles in the bearings 26, 26'. By means of the two pivotal movements 0, c and b, b all positions in arbitrary planes perpendicular to the shafts 12 or 12 for example GG and G,G,, can be attained. In the example of FIG. 11 the pivot points K, K are not at the same time the pivot points of universal joints; instead, the rotary shafts 2, 2' of the sickles are each driven by an electric motor 35, 35' and it is also possible to provide a suitable variable drive (not shown).

It may be mentioned that the co-operation of the mountings 8, 8' and the gear segments 14, 14' for adjusting the bevel gears l3, 13' makes it necessary that upon adjustment of the angle a by pivoting the mountings 8, 8' the segments 14, 14 will also be swung through the same angle; otherwise relative movement between the stationary gear segments and the adjusted mountings will cause the shafts 12, 12' to be turned by the gears 13, 13.

We claim:

1. Apparatus for cross-bottom folding the ends of flattened tube sections to be made into bags or sacks, the ends of said flattened tube sections being fed into said apparatus in a feeding plane in a feeding direction transverse to the sides of the tube sections, said apparatus comprising: first and second rotary shafts extending at an inclination with respect to one another and symetrically oriented with respect to said feeding plane; a spreader mounted on each of said rotary shafts, said Spreaders symetrically positioned with respect to said feeding plane; means for synchronously rotating said first and second rotary shafts during successive work cycles so that said spreaders are adapted to enter and spread the ends of the tube sections as said spreaders synchronously rotate with said rotary shafts; means pivotally mounting said first and second rotary shafts about respective pivot points disposed symetrically with respect to said feeding plane; and means for synchronously pivoting said rotary shafts in a predetermined pattern during each work cycle of said apparatus.

2. Apparatus according to claim 1 wherein the spreaders are sickle-shaped and attached to the rotary shafts by their sickle stems.

3. Apparatus according to claim 2 wherein the sickle stems are releasably attached to, and adjustable lengthwise of, the rotary shafts.

4. Apparatus according to claim 1 wherein said mounting means includes a pair of pivot shafts positioned parallel to said feeding direction, the axis of each pivot shaft passing through its respective pivot point; and wherein said pivoting means is adapted to cause said rotary shafts to pivot during the spreading operation in the sense of increasing their angles of inclination.

. 5. Apparatus according to claim. 4 wherein said mounting means includes a pair of bearings pivotable about respective of said pivot shafts; and wherein said rotary shafts are mounted in said bearings.

6. Apparatus according to claim 5 wherein said mounting means include gear teeth; and wherein said motive means act on said mounting means through said gear teeth.

7 Apparatus according to claim 5 wherein said mounting means include supporting arms pivotable about said pivot shafts such that said pivot shafts extend lengthwise of said supporting arms; and wherein said bearings are attached to said supporting arms.

8. Apparatus according to claim 7 further including: bevel gears attached to the pivot shafts of the supporting arms; bevel gear segments which are pivotable about respective stationary axes engaging said bevel gears; and a pivot drive operative in sequence with the work cycle of the apparatus attached to said bevel gear segments.

9. Apparatus according to claim 5 wherein said mounting means include supporting arms attached to said bearings and having slots concentric with the respective pivot points and by means of which the inclination of the spreaders is adjustable.

' 10. Apparatus according to claim 4 wherein each mounting means includes two perpendicular pivot shafts, the axis of each passing through the respective pivot points of said mounting means, said two perpendicular pivot shafts being perpendicular to the associated rotary shaft.

11. Apparatus according to claim 10 wherein said mounting means include supporting arms pivotable about said pivot shafts such that said pivot shafts extend lengthwise of said supporting arms; and wherein said bearings are attached to said supporting arms.

12. Apparatus according to claim 1 wherein said rotary shafts are pivotable along a substantially conical path about a straight line joining said pivot points, such that the point at which the spreaders come closest to one another during their rotation is displaced as said shafts are pivoted along said path.

13. Apparatus according to claim 12 wherein said motive means causes said point of closest approach to be displaced into each tube section end during entry of the spreaders into each tube section.

said mounting means includes a bearing mounting its associated rotary shaft; and a pivot shaft having an axis extending through both pivot points; said mounting means being movable in accordance with the desired displacement of the point of closest approach of the two spreaders.

16. Apparatus according to claim 15 wherein said mounting means include gear teeth; and wherein said motive means act on said mounting means through said gear teeth.

17. Apparatus according to claim 12 wherein each mounting means includes two perpendicular pivot shafts, the axis of each passing through the respective pivot points of said mounting means, said two perpendicular pivot shafts being perpendicular to the associated rotary shaft.

18. Apparatus according to claim 1 further including a drive for each rotary shaft, including; articulation means disposed at each of said pivot point.

19. Apparatus according to claim lfiwherein said articulation means comprise universal joints.

20. Apparatus according to claim 19 further including: a connecting shaft which interconnects and drives said universal joints; and a gear attached to said connecting shaft for driving same.

21. Apparatus according to claim 1, further including: first and second drive means, each drive means being connected to and pivotable with its associated rotary shaft, said drive means being synchronized with one another. 

1. Apparatus for cross-bottom folding the ends of flattened tube sections to be made into bags or sacks, the ends of said flattened tube sections being fed into said apparatus in a feeding plane in a feeding direction transverse to the sides of the tube sections, said apparatus comprising: first and second rotary shafts extending at an inclination with respect to one another and symetrically oriented with respect to said feeding plane; a spreader mounted on each of said rotary shafts, said spreaders symetrically positioned with respect to said feeding plane; means for synchronously rotating said first and second rotary shafts during successive work cycles so that said spreaders are adapted to enter and spread the ends of the tube sections as said spreaders synchronously rotate with said rotary shafts; means pivotally mounting said first and second rotary shafts about respective pivot points disposed symetrically with respect to said feeding plane; and means for synchronously pivoting said rotary shafts in a predetermined pattern during each work cycle of said apparatus.
 2. Apparatus according to claim 1 wherein the spreaders are sickle-shaped and attached to the rotary shafts by their sickle stems.
 3. Apparatus according to claim 2 wherein the sickle stems are releasably attached to, and adjustable lengthwise of, the rotary shafts.
 4. Apparatus according to claim 1 wherein said mounting means includes a pair of pivot shafts positioned parallel to said feeding direction, the axis of each pivot shaft passing through its respective pivot point; and wherein said pivoting means is adapted to cause said rotary shafts to pivot during the spreading operation in the sense of increasing their angles of inclination.
 5. Apparatus according to claim 4 wherein said mounting means includes a pair of bearings pivotable about respective of said pivot shafts; and wherein said rotary shafts are mounted in said bearings.
 6. Apparatus according to claim 5 wherein said mounting means include gear teeth; and wherein said motive means act on said mounting means through said gear teeth.
 7. Apparatus according to claim 5 wherein said mounting means include supporting arms pivotable about said pivot shafts such that said pivot shafts extend lengthwise of said supporting arms; and wherein said bearings are attached to said supporting arms.
 8. Apparatus according to claim 7 further including: bevel gears attached to the pivot shafts of the suppOrting arms; bevel gear segments which are pivotable about respective stationary axes engaging said bevel gears; and a pivot drive operative in sequence with the work cycle of the apparatus attached to said bevel gear segments.
 9. Apparatus according to claim 5 wherein said mounting means include supporting arms attached to said bearings and having slots concentric with the respective pivot points and by means of which the inclination of the spreaders is adjustable.
 10. Apparatus according to claim 4 wherein each mounting means includes two perpendicular pivot shafts, the axis of each passing through the respective pivot points of said mounting means, said two perpendicular pivot shafts being perpendicular to the associated rotary shaft.
 11. Apparatus according to claim 10 wherein said mounting means include supporting arms pivotable about said pivot shafts such that said pivot shafts extend lengthwise of said supporting arms; and wherein said bearings are attached to said supporting arms.
 12. Apparatus according to claim 1 wherein said rotary shafts are pivotable along a substantially conical path about a straight line joining said pivot points, such that the point at which the spreaders come closest to one another during their rotation is displaced as said shafts are pivoted along said path.
 13. Apparatus according to claim 12 wherein said motive means causes said point of closest approach to be displaced into each tube section end during entry of the spreaders into each tube section.
 14. Apparatus according to claim 12 wherein said motive means causes said point of closest approach to be displaced during each spreading operation opposite the direction of rotation of the spreaders.
 15. Apparatus according to claim 12 wherein each of said mounting means includes a bearing mounting its associated rotary shaft; and a pivot shaft having an axis extending through both pivot points; said mounting means being movable in accordance with the desired displacement of the point of closest approach of the two spreaders.
 16. Apparatus according to claim 15 wherein said mounting means include gear teeth; and wherein said motive means act on said mounting means through said gear teeth.
 17. Apparatus according to claim 12 wherein each mounting means includes two perpendicular pivot shafts, the axis of each passing through the respective pivot points of said mounting means, said two perpendicular pivot shafts being perpendicular to the associated rotary shaft.
 18. Apparatus according to claim 1 further including a drive for each rotary shaft, including; articulation means disposed at each of said pivot point.
 19. Apparatus according to claim 18 wherein said articulation means comprise universal joints.
 20. Apparatus according to claim 19 further including: a connecting shaft which interconnects and drives said universal joints; and a gear attached to said connecting shaft for driving same.
 21. Apparatus according to claim 1, further including: first and second drive means, each drive means being connected to and pivotable with its associated rotary shaft, said drive means being synchronized with one another. 